Electric rotating machine provided with a field control coil

ABSTRACT

In a rotating electric machine using permanent magnets and a field control coil, to allow the properties of the rotating electric machine to be readily changed and the rotating electric machine to be adapted to various applications even when it is made of common component parts, the field control coil is adapted to superimpose magnetic flux components of different intensities onto magnetic flux components that are supplied by the magnet poles and iron poles to the teeth, respectively. The magnetic flux components may be differentiated by placing each permanent magnet in a recess defined in an inner circumferential surface of the yoke, and defining each iron pole by a part of the yoke located between an adjacent pair of the permanent magnets in such a manner that the inner circumferential surface of each permanent magnet is lower than the said part of the yoke.

The present application claims priority from International ApplicationPCT/JP02/03030 filed on Mar. 28, 2002, which in turn claims priorityfrom Japanese Application 2001-092765, filed on Mar. 28, 2001.

TECHNICAL FIELD

The present invention relates to an electric rotating machine usingpermanent magnets for forming an electric field, and in particular to anelectric rotating machine suitable for use as a starter/generator whichcan be used both as a starter motor for starting an internal combustionengine and as a generator once the engine has started.

BACKGROUND OF THE INVENTION

A vehicle engine is typically provided with a starter motor for startingthe engine and a generator for generating electricity once the enginehas started, and the accessories of the engine can be made compact andlight in weight if these two pieces of equipment are combined into asingle unit. Based on such a view point, various proposals have beenmade to use an electric motor also as a generator. Such astarter/generator is, not exclusively, suitable for use in smallmotorcycles, and typically consists of an electric rotating machineusing permanent magnets for forming a magnetic field.

In such a starter/generator, it is necessary to generate as strong amagnetic field as possible for the given condition (size, weight, etc.)to the end of maximizing the output torque as a starter motor forstarting the engine, but a strong magnetic field also results in anexcessive generation of electricity when it is used as a generator.Therefore, the applicant previously proposed in Japanese patent laidopen publication No. 07-59314 to provide a field control coil andcontrol the strength of the magnetic field passing through the magnetpoles. The magnetic field produced by the field control coil partlycancels the magnetic field generated by the permanent magnets, andcontrols the generation of electricity when it is used as a generator.

However, the permanent magnets and field control coil are arranged indifferent locations, and a desired control of the magnetic field is notalways possible. Thus, it has not been possible to achieve both themaximization of output torque when used as an electric motor and thecontrolled generation of electricity when used as an electric generatorwithout involving an unacceptable compromise.

BRIEF SUMMARY OF THE INVENTION

In view of such problems of the prior art, a primary object of thepresent invention is to provide a rotating electric machine of a typeusing permanent magnets for generating a magnetic field which is adaptedto be readily modified of the properties thereof, and can be therebyadapted to different applications without substantially replacingcomponent parts thereof.

A second object of the present invention is to provide an improvedrotating electric machine of the above mentioned type provided with afield control coil which can be modified of the properties thereof overa wider range.

A third object of the present invention is to provide an improvedrotating electric machine which is suitable for use as a generator thatcan change the maximum capacity thereof in a favorable manner.

A fourth object of the present invention is to provide an improvedrotating electric machine which is suitable for use as astarter/generator for an internal combustion engine.

According to the present invention, such objects can be accomplished byproviding a rotating electric machine, comprising a stator including aplurality of teeth each having a coil wound thereon, a rotor includingpermanent magnet poles and iron poles arranged concentrically and in analternating fashion, and a field control coil for generating magneticflux that is superimposed on a magnetic field which the magnet poles andiron poles supply to the teeth, characterized by that: the field controlcoil is adapted to superimpose magnetic flux components of differentintensities onto magnetic flux components that are supplied by themagnet poles and iron poles to the teeth, respectively.

Thus, the control range possible for the field control coil can beexpanded for the given supply current by taking advantage of thesaturation of magnetic flux. Therefore, an electric rotating machinehighly suitable for a starter/generator for an internal combustionengine can be provided. Magnetic flux components of differentintensities can be overlaid to the magnetic field components which themagnet poles and iron poles supply to the teeth by using any one of anumber of possible means. For instance, by appropriately providingmagnetic resistances within the magnetic circuit, the intensities ofmagnetic flux components can be differentiated. A magnetic resistancecan be changed by selecting the material that is interposed in themagnetic circuit, by changing the air gap, or changing the size of themagnetic path such as the thickness and/or width of the part of the yokedefining the magnetic path.

In particular, in the case of a starter/generator for an internalcombustion engine, by making the air gap corresponding to the magnetpoles greater than that corresponding to the iron poles, the outputtorque as a starter motor can be maximized while the output as agenerator can be effectively controlled. According to such a preferredembodiment, each permanent magnet is placed in a recess defined in aninner circumferential surface of the yoke, and each iron pole is definedby a part of the yoke located between an adjacent pair of the permanentmagnets, an inner circumferential surface of each permanent magnet beingprovided with a height different from that of the said part of the yoke(for instance with a height lower than that of the said part of theyoke) whereby the magnetic flux components of different intensities aresuperimposed onto magnetic flux components that are supplied by themagnet poles and iron poles to the teeth, respectively.

The electric rotating machine of the present invention can be applied toboth outer rotor electric rotating machines and inner rotor electricrotating machines, and may be applied to normal electric motors,generators and engine starters as well as starter/generators.

BRIEF DESCRIPTION OF THE DRAWINGS

Now the present invention is described in the following with referenceto the appended drawings, in which:

FIG. 1 is a sectional vertical view showing a starter/generator (firstembodiment) embodying the present invention;

FIG. 2 is a fragmentary sectional view taken along line II—II of FIG. 1;

FIG. 3 is a diagram of a magnetic circuit including a permanent magnetand a field control coil serving as sources of magnetic flux;

FIG. 4 is a graph showing the distribution of effective magnetic fluxbetween iron poles and magnet poles;

FIG. 5 is a sectional vertical view showing another rotating electricmachine (second embodiment) embodying the present invention;

FIG. 6 is a sectional vertical view showing yet another rotatingelectric machine (third embodiment) embodying the present invention;

FIG. 7 is a sectional vertical view showing yet another rotatingelectric machine (fourth embodiment) embodying the present invention;and

FIG. 8 is a sectional vertical view showing yet another rotatingelectric machine (fifth embodiment) embodying the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a sectional side view of a starter/generator 1 embodying thepresent invention. This starter/generator 1 consists of an outer rotorrotating electric machine, and, for instance, comprises a stator 3fixedly attached to an end wall of an internal combustion engine E for asmall motorcycle via a bracket 2, and a rotor 5 fixedly attached to acrankshaft 4 of the engine E. The starter/generator 1 is used as anengine starter when starting the engine, and also as a generator forsupplying electricity to a battery not shown in the drawing and otherloads once the engine has started.

The stator 3 is provided with a core 6 which is fixedly attached to thebracket 2, and the core 6 is in turn provided with a prescribed numberof core teeth 6 a which project radially outwardly therefrom. A statorcoil 7 is wound around each core tooth 6 a. The rotor 5 comprises a bossmember 8 fixedly and coaxially attached to the crankshaft 4, and acup-shaped yoke 9 coaxially attached to the axially projecting end (leftend in the drawing) of the boss member 8. A prescribed number ofpermanent magnets 10 are attached to the inner circumferential surfaceof the yoke 9 circumferentially at an equal interval.

In this starter/generator 1, a field control coil 11 surrounding theboss member 8 is fixedly attached to the bracket 2, and the fieldcontrol coil 11 and stator 3 are received inside the yoke 9. Bysupplying electric current to the field control coil 11, a magnetic fluxpassing through the boss member 8, core 6 (core tooth 6 a) and yoke 9 isgenerated.

This starter/generator 1 is adapted to operate as a brush-less motor,and a sensor permanent magnet not shown in the drawing is provided onthe boss member 8 while a Hall device not shown in the drawing isprovided on the corresponding part of the bracket 2 so that a per seknown control of a brush-less motor may be effected.

In this starter/generator 1, as shown in FIG. 2, the permanent magnets10 are arranged on the inner circumferential surface of the yoke 9 in aspaced apart relationship with a same pole facing radially inward.Magnet poles 10 a defined by the inner surfaces of the permanent magnets10 and iron poles 9 a serving as control magnet poles and defined by theparts of the yoke 9 located between adjacent permanent magnets 10 opposethe stator 3 in an alternating manner. Each iron pole 9 a may be formedeither by a part of the yoke 9 projecting radially inwardly or by aseparate member which is fixedly attached to the yoke 9.

Thus, the magnetic flux generated by the permanent magnet 10 flows fromthe tooth 6 a to the magnet pole 10 a as indicated by arrow H₁ in FIG.3, and forms, on the one hand, a closed loop via the yoke 9, iron pole 9a, tooth 6 a, core 6, tooth 6 a and magnet pole 10 a as indicated byarrow H₂ and, on the other hand, a closed loop via the yoke 9, bossmember 8, core 6, tooth 6 a and magnet pole 10 a as indicated by arrowH₃. By supplying electric current to the field control coil 11, amagnetic flux passing the boss member 8, yoke 9 and core 6 (tooth 6 a)is generated, and this magnetic flux comprises magnetic flux componentsH₄ and H₅ passing through the magnet pole 10 a and iron pole 9 a,respectively. As will be discussed hereinafter, by supplying electriccurrent to the field control coil 11 and producing the magnetic fluxcomponents that are superimposed on the magnetic flux componentsgenerated by the permanent magnets 10, the magnetic field can becontrolled as desired.

This embodiment is described in more detail with reference to FIGS. 3and 4. When no electric current is supplied to the field control coil11, the magnetic flux component H₁ flows from the tooth 6 a to themagnet pole 10 a, and the magnetic flux component H₂ flows from the ironpole 9 a to the tooth 6 a. Therefore, the total swing of the magneticflux of the magnetic field is given by (H₁+H₂). When electric current ofa prescribed polarity is supplied to the field control coil 11 to usethe rotating electric machine as an engine starter or an electric motor,a magnetic flux component (H₁−H₄) flows from the tooth 6 a to the magnetpole 10 a, and a magnetic flux component (H₂+H₅) flows from the ironpole 9 a to the tooth 6 a. Therefore, the total swing of the magneticflux of the magnetic field is given by (H₁+H₂−H₄+H₅). When electriccurrent of the opposite polarity (electric current of the same amplitudeand opposite polarity was selected to simplify the discussion) issupplied to the field control coil 11 to use the rotating electricmachine as a generator, a magnetic flux component (H₁+H₄) flows from thetooth 6 a to the magnet pole 10 a and a magnetic flux component (H₂−H₅)flows from the iron pole 9 a to the tooth 6 a. However, from a practicaldesign consideration, the size of the core is minimized for the requiredmagnetic flux so that it is typical for the magnetic circuit includingthe core to saturate at the magnetic flux level of H₁. Therefore, inreality, the magnetic flux component that flows from the tooth 6 a tothe magnet pole 10 a is H₁ instead of (H₁+H₄). Therefore, the totalswing of the magnetic flux of the magnetic field is given by (H₁+H₂−H₅).$\quad\begin{matrix}\quad & \text{swing~~of~~the~~magnetic~~~~~flux~~of~~the~~field} \\\text{motor} & {H_{1} + H_{2} - H_{4} + H_{5}} \\\text{no~~electric~~current~~for~~the~~field~~coil} & {H_{1} + H_{2}} \\\text{generator} & {H_{1} + H_{2} - H_{5}}\end{matrix}$

Therefore, the difference in the swing of the magnetic flux of the fieldobtained by reversing the polarity of the field coil is given by(−H₄+2H₅). Here, the electric current had a same amplitude, and only itspolarity was reversed when selecting the use of the rotating electricmachine either as a starter motor or a generator in the foregoingexample, but the amplitude and polarity of the electric current can beselected individually and freely in practice.

In this embodiment, as shown in FIG. 2, the permanent magnet 10 isprovided in a recessed part of the inner circumferential surface of theyoke 9 opposing the tooth 6 a, and the gap Dm defined between the tooth6 a and the inner circumferential surface of the permanent magnet 10 isgreater than the gap Df defined between the tooth 6 a and the iron pole9 a. Therefore, the magnetic resistance Rm between the permanent magnet10 and tooth 6 a is greater than the magnetic resistance Rf between theiron pole 9 a and tooth 6 a. On the other hand, the gap Ds definedbetween the core 6 and the boss member 8 is common for the magnet pole10 a and iron pole 9 a, and therefore gives rise to a same magneticresistance Rs for these two poles 9 a and 10 a. In particular, becauseof the difference provided between the magnetic resistances Rm and Rf asmentioned above, H₅ is substantially greater than H₄. This causes thedifference in the swing of the magnetic flux to be made greateraccordingly.

Thus, by supplying electric current having a prescribed polarity andamplitude to the field control coil 11, the swing of the magnetic fluxof the field can be maximized so as to ensure an adequate output as anelectric motor, and by supplying electric current of the oppositepolarity to the magnetic field control coil 11, the swing of themagnetic flux of the field can be minimized so as to control the outputas a generator. Therefore, when this rotating electric machine is usedas a starter/generator, it is possible to obtain an adequate output as astarter and a properly controlled output as a generator by appropriatelyselecting the polarity and amplitude of the electric current that issupplied to the field control coil 11.

When the rotating electric machine is designed as an electric motor, itsproperty can be varied over a wide range by appropriately selecting thepolarity and amplitude of the electric current that is supplied to thefield control coil 11. Therefore, a compact and economical electricmotor having a large torque output can be achieved without undulyincreasing the size of the permanent magnets. In particular, by changingthe supply of electric current to the field control coil 11, theelectric rotating machine can be adapted to a wide range ofapplications. Likewise, when the rotating electric machine is designedas a generator, because the property can be controlled over a widerange, the dependency on a regulator circuit can be minimized or theneed for a regulator circuit can be even totally eliminated. Inparticular, when it is used as a generator for an internal combustionengine, the noise and fuel economy properties of the engine can beimproved. Furthermore, the rotating electric machine can be readilyadapted to the change in the required specifications without changingthe basic design. Also, when it is used as a starter motor of aninternal combustion engine, the same starter motor can be readilyadapted to engines of different specifications.

FIG. 5 shows a second embodiment of the present invention which isapplied to a generator using a slightly different yoke. In FIG. 5, theparts corresponding to those of the previous embodiment are denoted withlike numerals without repeating the description of such parts. Thisgenerator is provided with a second yoke 12 fixedly attached to the endbracket 2 of the engine or the like, in addition to a first yoke 11similar to that of the previous embodiment which is provided on the sideof the rotor 5. The second yoke 12 which is disposed coaxially inrelation to the rotor 5 is provided with the shape of a cylinder havinga closed bottom, and a boss member 12 a extends centrally and integrallyfrom the second yoke 12. The boss member 12 a extends along therotational center line of the rotor 5, and is connected to the centralinner circumference of the stator core 6 so that the boss member 12 aand the stator core 6 are magnetically connected to each other.

The inner bore of the fixed boss member 12 a receives a free end of theboss member 8 of the rotor 5, and a gap is defined between the innercircumferential surface of the fixed boss member 12 a and the outercircumferential surface of the boss member 8 of the rotor 5 tomagnetically insulate these two parts from each other. An additional gapis defined between the free end of the fixed boss member 12 a and thebottom of the first yoke 9 to magnetically insulate them from eachother. Thereby, the magnetic flux from the field control coil 11 isprevented from flowing into the boss member 8 of the rotor 5 and thebottom part of the first yoke 9. The bottom part of the second yoke 12is fixedly attached to the end bracket 2 by threaded bolts.

The second yoke 12 is provided with an outer cylindrical part 12 b whichsurrounds the outer cylindrical part of the first yoke 9 from theopposite side of the first yoke 9 or from the right hand side of thedrawing. An air gap is defined between the outer circumferential surfaceof the outer cylindrical part of the first yoke 9 and the outercylindrical part 12 b of the second yoke 12 so that the cylindrical partof the first yoke 9 along with the magnet poles 10 a and iron poles 9 ais received between the cylindrical part 12 b of the second yoke 12 andthe stator core 6. In other words, with the boss member 8 of the rotor 5received centrally in the fixed boss member 12 a of the second yoke 12,the rotor 5 is driven by a crankshaft or the like whereby the magnetpoles 10 a and iron poles 9 a rotate around the stator.

A field control coil 11 is disposed on a side of the stator core 6facing away from the first yoke 9, interposed between the stator core 6and the bottom part 12 a of the second yoke 12. The field control coil11 is wound around the fixed boss member 12 a, and the intensity andpolarity of electric current that is supplied to the field control coil11 can be appropriately controlled by a control circuit not shown in thedrawing. According to this generator, as opposed to the embodimentillustrated in FIGS. 1 and 2, wiring is not required to pass through thestator core 6 to reach the field control coil 11, and the wiringstructure can be thereby simplified as compared to the prior art.

According to the generator of this embodiment, the magnetic fluxgenerated by the field control coil 11 flows from the cylindrical part12 b of the second yoke 12 to the cylindrical part of the first yoke 9via an air gap while the boss member 8 of the rotor 5 is magneticallyinsulated from the boss member 12 a of the second yoke 12 via a gap sothat the magnetic flux generated by the field control coil 11 does notpass through the bottom part of the first yoke 9. In other words, themagnetic circuit (for which the field control coil 11 serves as amagnetic source) which was conventionally formed by the first yoke 9 isformed by the second yoke 12 in this case. Therefore, the bottom part ofthe first yoke 9 and the boss member 8 of the rotor 5 are relieved fromsuch a role, and the thickness of the first yoke 9 and the dimensions ofthe boss member 8 of the rotor 5 can be reduced so that the weight andinertia mass of the rotor 5 can be made comparable to those of theconventional motor not based on the hybrid field system.

Therefore, the hybrid field system can be applied to generators whichhave been considered as unsuitable because of the limitations associatedwith the inertia mass, and even such generators can be adapted to theproperty control thereof using a field control coil 11 and iron poles 6a. Furthermore, because the first yoke 9 and the boss member 8 of therotor 5 can be reduced in size, and the overall profile of the productcan be minimized.

Additionally, because the first yoke 9 and the boss member 8 of therotor 5 are not used as the magnetic path for the field control coil 11,these components may consist of those for more conventional generatorsnot based on the hybrid field system. In other words, the conventionalrotating electric machine can be used simply by arranging a combinationof permanent magnets and iron poles, instead of arranging permanentmagnets entirely along the inner circumference of the first yoke 9.Therefore, the first yoke 9 and the boss member 8 of the rotor are notrequired to be specially designed so as to make them match the fieldcontrol coil 11, and the production cost can be minimized because theexisting component parts and production facilities can be used withoutany modifications.

In this embodiment also, the permanent magnet 10 is provided in arecessed part of the inner circumferential surface of the yoke 9opposing the tooth 6 a, and the gap Dm defined between the tooth 6 a andthe inner circumferential surface (magnet pole 10 a) of the permanentmagnet 10 is greater than the gap Df defined between the tooth 6 a andthe iron pole 9 a. Therefore, the magnetic resistance Rm between thepermanent magnet 10 and tooth 6 a is greater than the magneticresistance Rf between the iron pole 9 a and tooth 6 a. Therefore, thisgenerator provides advantages similar to those that are achieved by theforgoing embodiment.

FIG. 6 shows a third embodiment of the present invention which isapplied to a brush-less motor. In FIG. 6, the parts corresponding tothose of the previous embodiment are denoted with like numerals withoutrepeating the description of such parts. This brush-less motor isprovided with a similar structure as the generator of the secondembodiment illustrated in FIG. 5, but the second yoke 12 serves as thecasing of the motor in addition to as the end bracket.

According to this motor, the rotor 5 is fixedly attached to a motorshaft 4, and is rotatably accommodated in a front bracket 13 made ofnon-magnetic material such as aluminum and an end bracket 12 servingalso as a second yoke. The front bracket 13 and end bracket 12 areattached to each other by fastening means not shown in the drawing withcylindrical parts 12 a and 13 a extending from these two parts abuttingeach other. The front bracket 13 is provided with a bearing 16, and theend bracket 12 is provided with a bearing 18 which is retained by abearing holder 17 made of non-magnetic material. The motor shaft 4 isrotatably supported by these bearings 16 and 18. This motor also allowsthe component parts of the conventional electric motor such as the rotor5 and the front bracket 13, and the existing production facilities to beused without any modification. The electric motor is thus assembled as asingle integral unit.

In this embodiment also, the permanent magnet 10 is provided in arecessed part of the inner circumferential surface of the yoke 9opposing the tooth 6 a, and the gap Dm defined between the tooth 6 a andthe inner circumferential surface (magnet pole 10 a) of the permanentmagnet 10 is greater than the gap Df defined between the tooth 6 a andthe iron pole 9 a. Therefore, the magnetic resistance Rm between thepermanent magnet 10 and tooth 6 a is greater than the magneticresistance Rf between the iron pole 9 a and tooth 6 a. Therefore, thisgenerator provides advantages similar to those that are achieved by theforgoing embodiments. Although this electric motor is based on thehybrid field system, the weight an inertia mass can be controlled to thelevels of the conventional electric motor, and an electric motor whoseproperties can be controlled at will can be used much in the same way asa more conventional electric motor. It should be appreciated that thisstructure is also applicable to electric generators.

FIG. 7 shows a fourth embodiment of the present invention which isapplied to a generator using a slightly different yoke. In FIG. 7, theparts corresponding to those of the previous embodiments are denotedwith like numerals without repeating the description of such parts. Asshown in FIG. 7, this generator consists of a stator 5 and a rotor 3. Inthis case, the rotor 5 serves as a field element, and the stator 3serves as an armature. This generator is based on the hybrid fieldsystem, and comprises a field control coil 11, and iron poles 6 aserving as control magnet poles similarly as the foregoing embodiments.

The rotor 5 comprises a boss member 8 which receives the crankshaft 4 ofan engine, for instance, in a fixed manner, and a first yoke 9 fixedlyattached to the outer surface of the boss member 8 of the rotor. Theboss member 8 of the rotor 5 is made of magnetic material such as iron,and is provided with a cylindrical shape. The boss member 8 of the rotorreceives the crankshaft 4 in a rotationally fast manner. The left end ofthe boss member 8 of the rotor is provided with a radial flange partwhich is provided with an annular connecting groove for fixedlyattaching the first yoke 9 thereto.

The first yoke 9 is made of magnetic material such as iron, and isprovided with the shape of a short cylinder having a closed end. Thefirst yoke 9 and the boss member 8 of the rotor are disposed in amutually coaxial relationship. The central opening of the bottom part ofthe first yoke 9 is fitted into the connecting groove, but otherpossible means may also be used for joining the first yoke 9 to the bossmember 8 of the rotor. The inner circumferential surface of the outercylindrical part of the first yoke 9 is provided with permanent magnets10 (magnet poles 10 a) and iron poles 9 a serving as control magnetpoles and formed by the material of the first yoke 9 along thecircumferential direction in an alternating fashion. The magnet poles 10a and iron poles 9 a jointly form the field element of the rotor 5. Inshort, this embodiment is also based on the hybrid field system, and thefield element is connected to a control unit. Additionally, similarly asthe embodiment illustrated in FIG. 2, the permanent magnet 10 isprovided in a recessed part of the inner circumferential surface of theyoke 9 opposing the tooth 6 a, and the gap Dm defined between the tooth6 a and the inner circumferential surface (magnet pole 10 a) of thepermanent magnet 10 is greater than the gap Df defined between the tooth6 a and the iron pole 9 a. Therefore, the magnetic resistance Rm betweenthe permanent magnet 10 and tooth 6 a is greater than the magneticresistance Rf between the iron pole 9 a and tooth 6 a. Therefore, thisgenerator provides advantages similar to those that are achieved by theforgoing embodiments.

The stator 3 comprises a stator core (core member) 6, a stator coil 7wound around each core tooth 6 a, and a second yoke 14 which is placedon the left end of the stator core 6 as seen in the drawing andmagnetically connected to the stator core 6. The stator core 6 is formedby laminating a number of thin plates of magnetic material such as iron.The stator core 6 is centrally provided with an opening for magneticallycoupling with the boss member 8 of the rotor via an air gap. The statorcore 6 is attached to the bracket 2 by at least three threaded bolts.

The second yoke 14 is also formed by laminating a number of thin platesof magnetic material such as iron, and comprises a main body having asmall diameter and opposing the boss member 8 via an air gap, and a diskpart 15 which extends from the upper most plate (the plate on the leftend) having an L-shaped cross section. A field control coil 11 is woundaround a shoulder part defined by the main body and disk part 15 of thesecond yoke 14 so as to surround the second yoke 14. Therefore, bysupplying electric current to this coil, the coil produces magnetic fluxcomponents which are superimposed on the magnetic field produced by thepermanent magnets 10.

One side of the disk part 15 extends in parallel with the inner surfaceof the bottom part of the first yoke 9, and a planar gap is definedbetween the side of the disk part 15 and the inner surface of the bottompart of the first yoke 9. The spacing of this gap can be selected atwill. By thus appropriately arranging the side of the disk part 15 andinner surface of the bottom part of the first yoke 9, the flow ofmagnetic flux from the disk part 15 of the second yoke 14 to the bottompart of the first yoke 9 can be effected in a uniform manner over theentire parts thereof.

In this embodiment also, the permanent magnet 10 is provided in arecessed part of the inner circumferential surface of the yoke 9opposing the tooth 6 a, and the gap Dm defined between the tooth 6 a andthe inner circumferential surface (magnet pole 10 a) of the permanentmagnet 10 is greater than the gap Df defined between the tooth 6 a andthe iron pole 9 a. Therefore, the magnetic resistance Rm between thepermanent magnet 10 and tooth 6 a is greater than the magneticresistance Rf between the iron pole 9 a and tooth 6 a. Therefore, thisgenerator provides advantages similar to those that are achieved by theforgoing embodiment. Therefore, this generator provides similaradvantages as the foregoing embodiments.

FIG. 8 shows a fourth embodiment of the present invention which isapplied to a generator using a slightly different yoke. In FIG. 8, theparts corresponding to those of the previous embodiments are denotedwith like numerals without repeating the description of such parts. Asshown in FIG. 8, this generator is provided with a second yoke 14similar to that of the previous embodiment, and an extension 15 a isadditionally provided along the outer periphery (free end) of the diskpart 15. One side of the extension 15 a extends substantially inparallel with the inner surface of the cylindrical part of the firstyoke 9. A suitable gap is defined between the side of the extension 15 aand the inner surface of the cylindrical part of the first yoke 9. Ascan be readily appreciated, the extension 15 a contributes to the flowof the magnetic flux component from the second yoke 14 to thecylindrical part of the first yoke 9, and thereby allows the weight ofthe boss member 8 and the first yoke 9 of the rotor 5 to be minimizedwithout reducing the effective magnetic flux.

INDUSTRIAL APPLICABILITY

Although the present invention has been described in terms ofapplications to electric generators and brush-less motors, the presentinvention can be applied to a wider range of rotating electric machinesusing permanent magnets provided on the side of the rotor, such asstarter/generators for motorcycles, portable generators, various utilitydevices using general purpose engines such as battery-less sprayingmachines, outer rotor fan motors, and so forth. In fact, the foregoingembodiments are applicable to all forms of rotating electric machines,and they may include both outer rotor and inner rotor rotating electricmachines. Also, the kinds of rotating electric machines of the presentinvention include, not exclusively, electric motors, generators, startermotors and starter/generators which serve the dual purposes of a startermotor and a generator.

1. A rotating electric machine, comprising: a stator including at leasta plurality of teeth each having at least a coil wound thereon, a rotorincluding at least permanent magnet poles and iron poles arrangedconcentrically and in an alternating fashion, and a field control coilfor generating magnetic flux that is superimposed on a magnetic field,which the magnet poles and iron poles supply to the teeth, wherein, thefield control coil is adapted to superimpose magnetic flux components ofdifferent intensities, onto magnetic flux components that are suppliedby said magnet poles and iron poles to the teeth, respectively, bydifferentiating magnetic resistances for magnetic paths that are formedby said field control coil, through providing different air gaps in thecorresponding magnetic paths, so as to pass through said magnetic polesand said iron poles.
 2. A rotating electric machine according to claim1, wherein the air gap for the magnet poles is greater than the air gapfor the iron poles.
 3. A rotating electric machine according to claim 1,wherein the rotating electric machine comprises an outer rotor rotatingmachine, and the rotor is provided with a central boss, and a yokehaving a cylindrical shape with a closed end which is coaxially attachedto the central boss, the magnet poles and iron poles being formed on aninner circumferential surface of the yoke.
 4. A rotating electricmachine according to claim 3, wherein each permanent magnet pole isdisposed in a recess defined in an inner circumferential surface of theyoke, and each iron pole is defined by a part of the yoke locatedbetween an adjacent pair of the permanent magnet poles, an innercircumferential surface of each permanent magnet pole being providedwith a height different than that of the said part of the yoke wherebythe magnetic flux components of different intensities are superimposedonto magnetic flux components that are supplied by the magnet poles andiron poles to the teeth, respectively.
 5. A rotating electric machineaccording to claim 1, wherein the inner circumferential surface of eachpermanent magnet is lower than the said part of the yoke.
 6. A rotatingelectric machine according to claim 1, wherein the rotating electricmachine includes at least an electric motor.
 7. A rotating electricmachine according to claim 1, wherein the rotating electric machineincludes at least an electric generator.
 8. A rotating electric machineaccording to claim 1, wherein the rotating electric machine includes atleast a starter motor.
 9. A rotating electric machine according to claim1, wherein the rotating electric machine includes at least a starter andgenerator.
 10. A rotating electric machine according comprising: a innerstator including a plurality of teeth each having a coil wound thereon,an outer rotor including at least a central boss and a yoke having acylindrical shape with a closed end which is coaxially attached to thecentral boss and permanent magnet poles and iron poles arrangedconcentrically and in alternating fashion on the inner circumference ofthe surface of said yoke, and a field control coil, for generatingmagnetic flux that is superimposed on a magnetic field which saidpermanent magnet poles and said iron poles supply to said teeth; andwherein each said permanent magnet pole is disposed in a recess definedin an inner circumferential surface of the yoke and each said iron poleis defined by a part of the yoke located between an adjacent pair ofsaid permanent magnet poles, an inner circumferential surface of eachsaid permanent magnet pole is provided with a height different than thatof the said part of the yoke whereby the magnetic flux components ofdifferent intensities are superimposed onto magnetic flux componentsthat are supplied by said permanent magnet poles and said iron poles tosaid teeth, respectively.
 11. A rotating electric machine according toclaim 10, wherein the magnetic flux components of different intensitiesare superimposed onto magnetic flux components that are supplied by themagnetic poles and iron poles to the teeth respectively, bydifferentiating magnetic resistances for magnetic paths that are formedby said field control coil so as to pass through the magnet poles andiron poles, respectively.
 12. A rotating electric machine according toclaim 11, wherein the magnetic resistances are differentiated byproviding different air gaps in the corresponding magnetic paths.
 13. Arotating electric machine according to claim 12, wherein, the air gapfor said magnet poles is larger than the air gap for said iron poles.14. A rotating electric machine according to claim 10, wherein the innercircumferential surface of each permanent magnet pole is lower than thesaid part of the yoke.
 15. A rotating electric machine according toclaim 10, wherein the rotating electric machine comprises an electricmotor.
 16. A rotating electric machine according to claim 10, whereinthe rotating electric machine comprises an electric generator.
 17. Arotating electric machine according to claim 10, wherein the rotatingelectric machine comprises a starter motor.
 18. A rotating electricmachine according to claim 10, wherein the rotating electric machinecomprises a starter and or generator.